The sight of Russia's Foreign Minister standing alongside the US Secretary of State, announcing an agreement over the future of Syria, will have delighted President Vladimir Putin.
By hurling Russian military might into Bashar al-Assad's struggle against his people, Putin has seized the ability to bargain on equal terms with America on the most urgent crisis in the Middle East. That alone will have justified the Geneva agreement in Putin's eyes.
But will the deal work? The accord that emerged from countless hours of talks between Kerry and his Russian counterpart, Sergei Lavrov, can be summarised as follows. If Assad's regime and his Russian allies will observe a ceasefire for seven days and allow the United Nations to dispatch aid convoys to besieged areas, then the Kremlin will be rewarded with military cooperation with the US.
In fact, Washington will open new vistas of battlefield intelligence. The US will tell Russia - and, by extension, Assad - what it knows about the precise locations of Jabhat Fateh al-Sham, once known as Jabhat al-Nusra, the branch of al-Qaeda in Syria, together with the positions held by "moderate" rebels.
In theory, this will allow Russia and the US to carry out coordinated air strikes against the former group while protecting the latter. But who can tell how that vital information, once handed over, might be used in future?
If the agreement falls apart, then Russia - and, by extension, Assad - will have gained a vital insight into the opposition, as well as Jabhat Fateh al-Sham. That could give them a crucial advantage when the fighting resumes.
At the very least, Russia and Assad will have discovered the state of US knowledge about Syria's array of rebels. If it turns out they know as much about their enemies as Washington, then Russia and Assad will still have learnt how much battlefield intelligence is held by America - and therefore by the US-led coalition in action over Syria and Iraq.
All that Russia and Assad have to do in return is to keep promises that have already been made and broken. Kerry's verbal summary of the Geneva agreement reads like a litany of old and ignored pledges.
A nationwide ceasefire? That was agreed in February - and broken by Assad and Russia within days. Allowing aid deliveries to besieged areas? That was a key provision of UN Resolution 2254, supported by Russia and the rest of the Security Council last December, urging all sides in the civil war to "immediately allow humanitarian agencies rapid, safe and unhindered access throughout Syria".
As for ending what Kerry called the "indiscriminate bombing of civilian neighbourhoods", these attacks are already banned under international humanitarian law. That has not stopped Russia and Assad from striking civilian targets with barrel bombs and poison gas.
So Russia and Assad are already pledged to observe a ceasefire, allow aid deliveries and stop slaughtering civilians from the air. With the Geneva agreement, they have promised good behaviour all over again. The difference is that if they cooperate this time, the US will provide information that could offer a vital advantage. And all that they have to do in return is restrain their forces for seven days. All that can go wrong is that Assad's obstinate and bone-headed regime will break the deal by continuing to rain barrel bombs on civilians. If so, America will have learnt that Putin cannot bend Assad to his will.
It is hard to avoid concluding that Kerry has been outplayed. In fairness, this was a reflection of the imbalance between the two sides. Russia is prepared to use force to achieve its aims in Syria, the most important of which is to save Assad's regime. The US will only mobilise its military prowess against Isis (Islamic State), not Assad.
Hence Kerry was starting from a disadvantage. If he had been able credibly to threaten the use of force against Assad - perhaps in retaliation for the pitiless denial of humanitarian aid to besieged areas - then the result might have been very different. But one of Kerry's hands had been firmly tied behind his back by President Barack Obama. Given that Obama is determined never to intervene against Assad, the best Kerry could do was achieve piecemeal gains - a ceasefire here, an aid convoy there. In the brutal politics of Syria's civil war, bargaining power grows from the barrel of a gun.